Resistance of the Archaeon Halococcus morrhuae and the Biofilm‐Forming Bacterium Halomonas muralis to Exposure to Low Earth Orbit for 534 Days

Abstract

The halophilic archaeon Halococcus morrhuae and the biofilm‐forming bacterium Halomonas muralis were exposed to space conditions during the EXPOSE‐R2 mission. Evidence for both strains co‐existing on a mural in the castle Herberstein (Austria) has been found and here we tested the theory that the biofilm produced by Hlm. muralis may act as a protective layer for Hcc. morrhuae during exposure to extreme conditions. During Pre‐flight tests it was shown that Hcc. morrhuae is significantly more resistant to extreme conditions compared to Hlm. muralis. A mixture of both strains proved advantageous only for the survival of Hcc. morrhuae. Hcc. morrhuae was exposed independently and in combination with Hlm. muralis to space conditions outside of the International Space Station (ISS) for 534 days. Survival of Hcc. morrhuae was investigated by most probable number test and colony‐forming unit assay; damage inflicted to genomic DNA was evaluated by random amplified polymorphic DNA‐PCR and the integrity of the 16S rRNA by real‐time PCR. Exposure to extreme conditions on Earth as well as in outer space had a strong detrimental effect on the survival and genomic stability of Hcc. morrhuae; however, we were able to re‐cultivate Hcc. morrhuae from samples exposed outside of the ISS.